Recently, in automobile navigation systems, positional information providing functions have been provided by which GPS signals transmitted from GPS satellites are received so as to acquire positional information of the own navigation systems and to indicate present positions on maps. Very recently, even in portable terminal apparatus such as portable telephones, such notification services as positional information and time instants may be provided by utilizing the GPS satellites.
Since GPS signals are employed, correct positional information such as latitude/longitude as to present positions may be acquired in higher precision. However, in such a case that a user travels by receiving only such GPS signals, the user cannot grasp that this traveling user is presently directed to which direction. In order to increase an additional value of positional information services provided in portable terminal apparatus, similar to automobile navigation systems, such a function is desirably employed. That is, while a geomagnetic sensor is employed so as to also acquire azimuth information, a map is rotated to be displayed in conjunction with such a direction to which a user is presently directed when a present position is displayed on the map.
However, as previously explained, in the case that a geomagnetic sensor is provided in a portable terminal apparatus so as to acquire azimuth information, there is such a risk that the geomagnetic sensor is adversely influenced by magnetic fields generated from other components, and thus, cannot correctly sense the geomagnetism. Since a large number of components for generating magnetic noise such as a speaker are mounted within the portable terminal apparatus, and furthermore, the respective mounted components are provided in the vicinity of each other so as to make this portable terminal apparatus compact, this geomagnetic sensor is brought into such a condition that the geomagnetic sensor may be adversely and readily influenced by magnetic noise. Also, while the portable terminal apparatus is carried by the user, another adverse influence caused by externally-applied magnetization must be considered. As a consequence, in order to achieve stable performance of the geomagnetic sensor, both a component arrangement and a structure, capable of avoiding an adverse influence caused by peripheral magnetic fields other than the geomagnetism, must be employed, so that designing of these component arrangement and structure is largely restricted.
In this case, FIG. 8 and FIG. 9 shows a structural example of a portable terminal apparatus equipped with both a GPS receiving unit and a geomagnetic sensor. This structural example indicates such a construction which is applied to a portable telephone arranged in that both a first housing 101 and a second housing 102 can be folded at a hinge portion 103. As indicated in FIG. 8(A), a GPS receiving unit 105 is provided on the first housing 101. The GPS receiving unit 105 is equipped with both a GPS antenna and a receiving circuit, which may receive a GPS signal 121 transmitted from a GPS satellite 120 so as to acquire positional information of the own portable telephone. Also, a geomagnetic sensor 107 for sensing geomagnetism is provided on a circuit board 32 in the second housing 102. The circuit board 106 mounts thereon a high frequency circuit, a baseband circuit, a control circuit, and the like, and is stored in this second housing 102. As this geomagnetic sensor 107, such a sensor is employed which is equipped with magnetic field detecting capabilities for two-axial components of the horizontal direction. Based upon the positional information acquired by the above-explained GPS receiving unit 105 and the azimuth information acquired by the geomagnetic sensor 107, the positional information and a time instant may be displayed on the display unit 108 in combination with a map.
Also, a speaker 109 is provided as a built-in component in the second housing 102 in the vicinity of the geomagnetic sensor 107, while this speaker 109 produces ringing sound (telephone calling sound), and the like. Magnetic noise radiated from a magnet 109a of this speaker 109 is expressed by a magnetic force line 110. As indicated in FIG. 8(B), a tangential vector 111 of the magnetic force line 110 radiated from the speaker 109 with respect to the geomagnetic sensor 107 contains both a vertical-direction component 111a and a horizontal-direction component 111b of the magnetic force line. As a consequence, the geomagnetic sensor 107 may sense this horizontal-direction component 111b of the magnetic force line 110, and thus, there is such a problem that the geomagnetic sensor 107 may produce errors in the geomagnetic detecting operation by receiving the adverse influence of the peripheral magnetic force, and cannot correctly sense the geomagnetism.
To cancel the adverse influence caused by this peripheral magnetic force, the arranging construction must be changed, for instance, such a component for giving an adverse influence to the geomagnetic sensor is separated from this geomagnetic sensor. Also, a correcting function by way of software must be provided. Alternatively, such a function capable of de-energizing the magnetic noise other than the geomagnetism must be mounted. Since such a means is employed, various problems may occur, for example, the above-described arranging construct can be hardly employed in the actual apparatus, and the apparatus becomes bulky and complex. Thus, such a means can be hardly applied to portable terminal apparatus.
Also, as represented in FIG. 9, in such a structural case that an antenna 115 is provided on the side of the second housing 102, when the portable telephone is put on a desk 125, a bottom plane (namely, plane on the outer side) of the second housing 102 cannot become flat, so that the geomagnetic sensor 107 provided inside the second housing 102 is inclined with respect to the horizontal plane. When the geomagnetic sensor 107 is inclined at an angle larger than, or equal to a predetermined angle, an error may occur in the geomagnetic detecting operation. In particular, when the geomagnetic sensor 107 is adjusted (calibrated) prior to the geomagnetic detecting operation, if the geomagnetic sensor 107 is inclined, then there is such a problem that the adjustment of the geomagnetic sensor 107 cannot be correctly carried out but the sensing precision of the geomagnetism is lowered.
The present invention has been made to solve the above-described problems, and therefore, has an object to provide a portable terminal apparatus capable of detecting geomagnetism in higher precision and capable of acquiring correct azimuth information, while eliminating an adverse influence caused by magnetic noise with respect to a geomagnetic sensor provided in a housing of the portable terminal apparatus.